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drm/amdkfd: avoid recursive lock in migrations back to RAM
[Why]: When we call hmm_range_fault to map memory after a migration, we don't expect memory to be migrated again as a result of hmm_range_fault. The driver ensures that all memory is in GPU-accessible locations so that no migration should be needed. However, there is one corner case where hmm_range_fault can unexpectedly cause a migration from DEVICE_PRIVATE back to system memory due to a write-fault when a system memory page in the same range was mapped read-only (e.g. COW). Ranges with individual pages in different locations are usually the result of failed page migrations (e.g. page lock contention). The unexpected migration back to system memory causes a deadlock from recursive locking in our driver. [How]: Creating a task reference new member under svm_range_list struct. Setting this with "current" reference, right before the hmm_range_fault is called. This member is checked against "current" reference at svm_migrate_to_ram callback function. If equal, the migration will be ignored. Signed-off-by: Alex Sierra <alex.sierra@amd.com> Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
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3 changed files with 8 additions and 0 deletions
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@ -861,6 +861,11 @@ static vm_fault_t svm_migrate_to_ram(struct vm_fault *vmf)
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pr_debug("failed find process at fault address 0x%lx\n", addr);
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return VM_FAULT_SIGBUS;
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}
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if (READ_ONCE(p->svms.faulting_task) == current) {
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pr_debug("skipping ram migration\n");
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kfd_unref_process(p);
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return 0;
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}
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addr >>= PAGE_SHIFT;
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pr_debug("CPU page fault svms 0x%p address 0x%lx\n", &p->svms, addr);
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@ -768,6 +768,7 @@ struct svm_range_list {
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atomic_t evicted_ranges;
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struct delayed_work restore_work;
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DECLARE_BITMAP(bitmap_supported, MAX_GPU_INSTANCE);
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struct task_struct *faulting_task;
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};
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/* Process data */
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@ -1496,9 +1496,11 @@ static int svm_range_validate_and_map(struct mm_struct *mm,
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next = min(vma->vm_end, end);
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npages = (next - addr) >> PAGE_SHIFT;
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WRITE_ONCE(p->svms.faulting_task, current);
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r = amdgpu_hmm_range_get_pages(&prange->notifier, mm, NULL,
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addr, npages, &hmm_range,
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readonly, true, owner);
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WRITE_ONCE(p->svms.faulting_task, NULL);
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if (r) {
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pr_debug("failed %d to get svm range pages\n", r);
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goto unreserve_out;
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